THE INMAN DIARY A Public and Private Confession. Edited by Daniel Aaron. Harvard University Press. Two volumes. 1,661 pp. $39.95.ddow

SAY HELLO to Arthur C. Inman, a monster of selfishness and a new and strange figure in 20th-century American literature.

Arthur shot himself in 1963, leaving behind an enormous literary monument -- a diary of 17 million words recording in extravagant detail an eccentric life chiefly spent in a cheap Boston apartment house called Garrison Hall. From this avalanche, the Harvard literary historian Daniel Aaron has quarried these two handsome volumes.

The Inman Diary succeeds in spite of its hero. Arthur -- not to beat around the bush -- is a creep. Chronic invalid and whiner, he uses poor health to get his way. He browbeats his wife, lives off his wealthy father and looks down on the poor. He hoards food during World War II and cheers the Axis on. He cadges sexual favors from his nurses.

While other men work, Arthur writes away at his giant diary, his "thrashing snake" of a record. It is, so to speak, his occupation, his raison d'etre. The diary has an unexpected effect on the reader. Gradually, despite everything, despite all the pettiness this distasteful man is capable of, we grow to like him. He makes us laugh. So the secret in reading The Inman Diary is perseverance. It really tells a tragicomic story revealed in its full dimensions only at the end of Arthur's life. Aaron's claims for this sprawling journal are sensibly modest. "What I am sure of," he writes, "is that the many-faceted mind of the diarist, the classic 'sick soul,' is presented with a disturbing fidelity and the promiscuous crowd passing in and out of Garrison Hall abounds with life."

The Inman Diary tells Arthur's history chronologically. An only child, he was born in 1895, into a prominent Atlanta family. Everything in his childhood was remembered and meticulously set down in later life. The Diary begins in 1919, after Arthur had suffered a physical and mental breakdown at Haverford College. Using his illness as a weapon, he is able to break free of his despised parents. Sent to Boston for medical treatment, he sets up an independent household. For the next half-century he lives the pampered life of an invalid, renting as many as five apartments at one time in Garrison Hall, on St. Botolph Street in Boston's South End, just south of the present Prudential Center. He suffers from extreme sensitivity to light and noise, migraine headaches and, mysteriously, "slipping bones and loose joints."

Surrounded by a retinue of physicians, readers, chauffeurs, cooks, secretaries and companions, helped by his long-suffering wife Evelyn, Arthur endures, in Aaron's phrase, "the last vestiges of eighteenth-century medcal lore." A regime of stomach pumpings, throat paintings, laxatives, emetics and enemas and the pokes, probes and stretches of many osteopaths keep Arthur's anxieties at bay. The story of his tempestuous relations with his wife reads like a novel. If the Diary were in fact a novel, its climax might be the enraged revelation that Arthur's favorite osteopath and best friend has seduced his wife and had secret sexual relations with her over a period of many years. Arthur is mighty hurt.

Not that Arthur is above a secret tumble himself. His sport and pastime is to caress and excite members of the ever-changing corps of female "younglings" who read aloud to him at night, alternately attracted and repelled by the giggling, talkative man on the big bed in the dark room. This activity grows more frequent as Arthur grows older, and as he and Evelyn become more and more estranged. By no means, however, should the Diary be considered a record of sexual voyeurism. In truth, large sections -- long, long sections -- of the abridged diary are of stupefying dullness.

In these pages, Arthur records his hatred of his father, his mother, landlords, real estate developers, children, the Irish, blacks, Jews, Catholics, dogs, Mayor James Curley, Franklin Delano Roosevelt ("Roosie the Rat"), T.S. Eliot and W.B. Yeats. He admires Hitler, Mussolini and Stalin. He adores money and speculates in the stock market. He yearns for fame. He frets over getting parts for his 1920 Cadillac, nicknamed "The Baby Carriage." He edits a volume of Confederate general George E. Pickett's letters, with which he takes shameful editorial liberties to jazz up the prose. He writes several books of spectacularly bad poetry; here is his poem "Ho for the Road":

Ho, for the road once more!

Ho, for the winged dawn!

Ho, for the larks' clear flight,

Caroling the day reborn! Ho, for the road once more!

Ho, for the drifted skies!

Ho, for the distant hills,

Purple where sunset dies!

CLEARLY PSYCHIATRISTS will have a field day with Arthur. The Yale historian of medicine, David F. Musto, in an appendix, cautiously inclines to the "possibility" that Arthur suffered from some "mild" form of a connective tissue disorder. More confidently, he asserts that Arthur's life was "cruelly complicated by medical mistreatment and by excessive, chronic ingestion" of bromides and alcohol.

Toward the end, Aaron spends a lot of time analyzing Arthur and not letting him tell the story. There is perhaps a touch of Harvard condescension toward a townie. The annotation contains some startling errors -- "The end came on Thursday, December 5, the same day President Kennedy's assassin was shot in a Dallas jail"; Lee Harvey Oswald was of course shot by Jack Ruby on Sunday, November 24.

Nevertheless, in its vivid portrayal of little people, ordinary people who are never famous for 15 minutes, or achieve any kind of professional or personal fame, The Inman Diary contains considerable literary gold hidden in the folds of its prolixity.

Arthur knew he was a failure. The experience turned him into a pessimist. "You come; you push years behind you; you approach an end: Eventually you end. And that's the whole of it. Leave behind your jet trail, and what's that worth save a star-like line across a blue firmament?" There are many such eloquent reflections in the Diary, and some fine lyricism, too -- in these pages the sea gulls wheel and dive over Boston Harbor and the hidden lives ashore. And so this history of the messy lives at Garrison Hall achieves a certain splendor. No doubt it will live on as a literary curiosity, a cult masterpiece, Arthur's bid for immortality as the Saint-Simon of the South End.